Laser applications can be divided into several general categories including the measurement of spatial parameters, material heating and/or removal, non-destructive probing of resonant phenomena, communications, optical processing, laser-induced chemical reactions and weapons.
The combination of a laser with a flexible laser beam delivery system which may include a robot allows the laser to operate with a degree of freedom previously unknown. The combination of the two technologies, if successfully performed, is suitable for many material heating and/or removing applications such as cutting glass and trimming plastic or composites. For trimming complex contoured structures, a laser can be coupled with a five axis beam delivery device.
In any such beam delivery device it is important to have smooth device motion with high acceleration. For any specific material to be cut, there is a range of speeds that produce the best finish. Whenever there is a change in direction, the motion system must maintain this speed or cut quality will suffer.
Popular uses for metal-working lasers include seam, spot and fusion welding, cutting, drilling, surface hardening, metal marking, scarfing, deburring, trimming and heat treating. Metal cutting with a laser beam involves focusing the beam at a point on the surface of a workpiece and manipulating the beam to trace the desired cutting path.
NC machines are often used for cutting substantially flat surfaces with a laser beam. The beam path is usually fixed and the object to be cut is fixed to the NC machine table for manipulation in two orthogonal directions.
For cutting circular holes, the NC machine table is usually run at relatively low cutting speeds to maintain the accuracy of a circular pattern equivalent to that of a circular mechanical punch. The relatively large mass and high inertia of NC machine slides does not allow the machine to operate at the high speeds at which laser beam cutting is desired. Running NC machines at the high linear cutting speeds (possible with high power lasers), results in undesirable pattern distortions. Reaction forces from the table drive can induce vibrations in the beam delivery support structure. This will be seen as roughness in the cut. The situation is similar when prior art delivery systems utilizing robots are used to manipulate laser beams though the pattern distortion can be even worse.
One method for overcoming this problem is to use the NC machine or robot only to position the beam at the center point of the desired hole. An end effector of the delivery system offsets the beam focal point at the desired hole radius and then spins the beam itself about the center point of the circle. The focal point traces a circle and effects the desired cut. Higher speeds are attainable by virtue of the relatively low mass and inertia of the parts of the end effector moved in this condition.
An example of such an end effector is illustrated in FIG. 1, wherein four mirrors offset the beam to the desired radius. A linear slide provides adjustment of hole radius either in a programmable or manual fashion.
High quality laser beam cutting usually requires an adaptive focusing device to help maintain the optimum location of the focal point of the beam at the surface of the object being cut. Surface modulations are usually sensed by a variety of commercially available sensors and a control device is commanded to move the focal point towards or away from the surface in accordance with surface modulations. This requires that the beam focusing device or the object be moved as disclosed in U.S. Pat. No. 4,764,655 and U.S. Pat. No. 4,761,534.
Prior art NC machines usually add another axis of control to move the laser head and the focusing device in response to a surface sensor signal. Other prior art utilizes a focusing arrangement by which the focusing lens is moved along the beam center line in response to the surface sensor signal. This is highly desirable since the movable parts are light and can be moved responsively at higher speed than when the hole object, or the laser head, is moved. In combination with a hole cutting arrangement, however, this approach becomes quite complex.
One laser beam delivery system which moves a laser beam to perform an operation on a workpiece includes two mirrors in each joint (i.e. optical joint) of a tubular linkage mechanism which is manipulated by a robot to direct the laser beam along the desired path. A focusing lens positioned in the mechanism concentrates the laser energy and directs it to a singular point with a high power density. However, the robot must be very accurate to direct the beam to a precise area on a workpiece. A longer focal length lens could be used to compensate for robot inaccuracies. However, the resulting beam would be focused over a large area so that both power density and speed are lower.
Elimination of even one mirror from the total number of mirrors in a laser beam delivery system is important for the following reasons: (1) significant cost savings can be realized due to the relatively high cost of the mirrors compared to other components of the system; (2) the efficiency of power transmission is increased since power losses of the collimated laser beam are almost entirely attributed to the absorption of energy which occurs at each mirror; (3) initial alignment of the beam delivery system is simplified with fewer mirrors to align, thereby minimizing the magnitude of the resultant alignment error which is practically achievable; and (4) system reliability is increased and a reduction in required maintenance is achieved with fewer mirrors to clean and maintain in alignment.
The Plankenhorn U.S. Pat. No. 4,539,642 discloses a method of linking a robot with a laser including a laser arm which is manipulated by the robot. The laser arm is supported by the robot arm and is aligned to move in synchronization with the robot joints. The laser arm must be mounted to the robot arm in a precision synchronized fashion.
The Akeel U.S. Pat. No. 4,560,952 discloses a robot laser system including a laser wrist mechanism wherein the robot has a number of degrees of freedom constituted by two orthogonally related linear movements along intersecting longitudinal axes. The wrist has two orthogonally related rotary joints having intersecting pivotal axes.
The Monteith et al U.S. Pat. No. 4,707,585 discloses a laser robot system including a laser wrist.
The Bisiach U.S. Pat. No. 4,677,274 discloses a robot laser system wherein the laser beam reaches the robot through a side opening therein whereafter it is axially directed by a pair of adjustable mirrors to a hollow head.
The Libby U.S. Pat. No. 4,413,180 discloses image acquisition apparatus utilizing a hollow motor shaft through which a light beam enters. The light beam is then reflected by a concave cylindrical reflector to an intercept.
The Marinoni U.S. Pat. No. 4,698,483 discloses a robot laser system wherein the robot includes a base and a fork element supported vertically and rotatably by the base. An arm is articulated at its first end to the fork element about a substantially horizontal axis. A forearm is articulated to a second end of the arm about a substantially horizontal axis. A wrist assembly is mounted at the unarticulated end of the forearm, is rotatable about an axis parallel to the forearm and has an end portion which supports a lens for focusing the laser beam.
The Rando et al U.S. Pat. No. 4,698,479 discloses the use of sealed, sliding telescoping tubes in a laser beam delivery system.
Japanese Patent Document Ser. No. 59-107785 discloses a laser robot system including a robot having a motorized multi-joint arm provided with reflecting mirrors at the ends of the arm part.
Japanese Patent Document No. 59-223188 discloses a laser beam machine having a reflecting mirror provided in each joint portion of a manipulator.
The Rexer et al U.S. Pat. No. 3,986,767 discloses an optical focus device including focus and turning mirrors capable of rotating a laser beam about two orthogonal axes.